Nuclear Theory·nucl-th

Wed·Sep 16, 2026Wednesday·September 16, 2026

25 papers—11 primary·14 cross-listed

01
Obtaining tensor-polarized nuclei with spin $S \geq 1$ via spin filtering upon nuclear beam transmission through an unpolarized target (spin dichroism effect)
Sergey Anishchenko · Vladimir Baryshevsky · Alexandra Gurinovich
Upon transmission through an unpolarized target initially unpolarized nuclei with spin $S \geq 1$ acquire tensor polarization due to spin dichroism effect. For nuclei passing several nuclear lengths in the target, the acquired component $p_{z z}$ can reach substantial values of ~0.2-0.8. The beam obtained in this way can be effectively used to study reactions with tensor-polarized nuclei.
nucl-thhep-phnucl-ex
02
Comprehensive study of $Υ$ ( $n$ S) production in Oxygen+Oxygen collisions at LHC
Sabin Thapa · Biaogang Wu · Ramona Vogt · Ralf Rapp
We study bottomonium $Υ$ ( $n$ S) production in $O + O$ collisions at $s_{N N} = 5.36$ ~TeV, including both cold nuclear-matter (CNM) effects and final-state interactions in a short-lived quark-gluon plasma. The CNM baseline is calculated using the EPPS21 nuclear parton distribution functions together with coherent energy loss and transverse momentum broadening. Hot-medium effects are evaluated with two transport approaches coupled to the same centrality-resolved 3+1D aHydroQP background: the QTRAJ-NLO open-quantum-system calculation, implemented with the {\sc QTraj} code, and the TAMU-NP semiclassical rates, including primordial suppression and regeneration. The CNM effects give a moderate, state-independent suppression, dominated by the nPDF modification. The energy loss and transverse momentum broadening contribution remains at the few-percent level. Both transport approaches predict a sequential suppression pattern, $R_{AA}^{Υ (1 S)} > R_{AA}^{Υ (2 S)} > R_{AA}^{Υ (3 S)}$ , with the strongest suppression around midrapidity in central collisions. The suppression of the ground state is similar in the two approaches but differs for the excited states. Since the CNM factor is common to all states, double ratios provide a direct measure of the relative hot-medium suppression. Our results support the conclusion that $O + O$ collisions at the LHC can produce a short-lived QGP capable of modifying bottomonium yields.
nucl-thhep-ph
03
The chiral filter
Tae-Sun Park
Thermal neutron capture on a proton, $n p \to d γ$ , is measured to a fraction of a percent; the impulse approximation misses nine percent of it. This article follows that gap through five decades of an idea of Mannque Rho's, the chiral filter. Chiral symmetry fixes the pion-exchange current that fills the gap, and power counting explains why nothing else competes. The missing nine percent becomes a prediction, correct within errors. On the unprotected side, one constant fixed by tritium beta decay predicted solar $pp$ fusion and the {\it hep} process; $g_{A}^{*}$ remains open.
nucl-th
04
A general decay form and absolute nuclear stability
Wenqiang Zhang · Chong Qi
A nucleus is conventionally called stable when no decay has been observed. We replace this phenomenological definition with a criterion based on conservation laws alone. For this purpose, we formulate a general decay form (GDF) for finite charge-neutral nuclear systems that includes all possible final configurations allowed by known conservation laws. A nucleus is absolutely stable if no allowed configuration has lower mass. A global search over all nuclei with measured atomic masses yields 84 absolutely stable nuclei. Beyond the criterion of absolute stability, we introduce a dimensionless decay-accessibility entropy SGDF to quantify the relative accessibility of GDF-allowed decay channels. We rank all naturally occurring isotopes according to their maximum SGDF values and predict their dominant decay modes and corresponding partial half-lives. We further identify promising candidates for natural alpha and two-neutrino double-beta decays. The resulting framework also provides a nuclear-scale perspective on the far-future evolution of matter, in which nuclear decay drives matter toward combinations of these 84 absolutely stable nuclei before still slower forms of matter evolution. These findings extend the conventional phenomenological stable-radioactive classification to a conservation-law-based framework for nuclear stability and provide a quantitative roadmap for future rare-decay searches.
nucl-th
05
The Fock representation of the Coulomb interaction. I. Two-body problem
M. M. Nishonov
The unscreened Coulomb interaction is exactly separable in momentum space at negative energies, by the stereographic projection of Fock, with analytic form factors and strengths. It is derived here as an operator identity for the potential and added, without screening or fitting, as a block of separable terms to the separable nuclear input of a charged pair. The representation is compared with the screening--renormalization method and with Coulomb-distorted form factors on two-body benchmarks: the off-shell $t$ ~matrix, the Coulomb displacement of the $α p$ Pauli-forbidden state, and the Coulomb-modified phases of the $pp$ , $α p$ and $α α$ pairs. The Feshbach--Schur projection of the Pauli-forbidden state is shown to require the Coulomb-dressed eigenstate, which the Fock block provides within the same separable problem. At positive energy a finite truncation is a screened Coulomb potential with an analytic, momentum-dependent radius.
nucl-th
06
Revisiting nuclear chirality in $^{128}$ Cs with relativistic configuration-interaction density functional theory
Yakun Wang
Nuclear chirality in $^{128}$ Cs is revisited within the microscopic relativistic configuration-interaction density functional (ReCD) theory. The positive-parity doublet bands are investigated by simultaneously examining their energy spectra, electromagnetic transition probabilities, $g$ factors, spectroscopic quadrupole moments, and underlying angular-momentum geometry. Without introducing additional parameters adjusted to the spectroscopic data, the ReCD calculations provide an overall satisfactory description of the available experimental observables. In particular, a comprehensive analysis of the available experimental data and the calculated spectroscopic observables indicates qualitative resemblances between the partner bands around $I = 17ℏ$ . A microscopic analysis of the angular-momentum geometry through \textit{azimuthal plots} reveals a distinct evolution of the rotational mode with increasing spin: chiral vibration at $I < 17ℏ$ , static chirality at $I = 17ℏ$ , and a transition toward planar rotation at higher spins. These results suggest that static chiral geometry in $^{128}$ Cs is confined to a narrow spin region around $I = 17ℏ$ within the present ReCD calculations.
nucl-th
07
Alpha-Core Breakup in the Strong Decay of ${}_{\Lambda\Lambda}^{6}\mathrm{He}$ to a Deeply Bound $H$ Dibaryon
Mahboubeh Shahrbaf · Makoto Oka
We investigate the effect of $α$ -core breakup on the strong conversion of ${}^{6}_{\Lambda\Lambda}\mathrm{He}$ into a deeply bound $H$ dibaryon. In addition to the coherent $H+{}^{4}\mathrm{He}$ channel, we evaluate the open final states $H+p+{}^{3}\mathrm{H}$, $H+n+{}^{3}\mathrm{He}$, and $H+d+d$ using a translationally invariant Gaussian cluster description, including spin-isospin recoupling and full nonrelativistic three-body phase-space integrations. The breakup widths are normalized to Gal's intact-$\alpha$ result. At $B_{\Lambda\Lambda}^{H}=176~\mathrm{MeV}$, corresponding to $m_H\simeq2055~\mathrm{MeV}$, the summed breakup width exceeds the intact-$\alpha$ width by a factor $R_{\mathrm{br}}=2.49\times10^{3}$. The resulting inclusive width and lifetime are $\Gamma_{\mathrm{inc}}=3.87\times10^{-4}~\mathrm{eV}$ and $\tau_{\mathrm{inc}}=1.70\times10^{-12}~\mathrm{s}$, respectively, compared with $\tau_{\alpha}=4.25\times10^{-9}~\mathrm{s}$ for the intact-$\alpha$ channel alone. The mass-dependent calculation shows that the inclusive lifetime crosses the characteristic hypernuclear weak-decay timescale near $m_H\simeq2020~\mathrm{MeV}$ and increases rapidly as the $H$ mass decreases. In the representative dark-matter-motivated interval $1865\leq m_H\leq1885~\mathrm{MeV}$, we obtain $6.59\times10^{-4}\lesssim\tau_{\mathrm{inc}}\lesssim 6.80\times10^{-3}~\mathrm{s}$, far exceeding the weak-decay timescale. Thus, although core breakup can dominate the inclusive strong width near $m_H\simeq2055~\mathrm{MeV}$, weakly decaying double-$\Lambda$ hypernuclei remain compatible, within the present framework, with a deeply bound $uuddss$ state in the mass range relevant to sexaquark dark matter.
nucl-th
08
Imprints of the nuclear liquid-gas phase transition on net-baryon number fluctuations
Mattia Recchi · Shi Yin
We investigate net-baryon number fluctuations in the high-density, low-temperature region of the QCD phase diagram using the parity-doublet model (PDM) under the mean-field approximation. We compute the fluctuation ratios up to sixth order around the nuclear liquid-gas (LG) phase transition, where the high-order ratios are particularly sensitive. To connect the results with heavy-ion experiments, we test several different scenarios of chemical freeze-out. We find that near the LG transition the extracted fluctuations depend strongly on the choice of freeze-out curve. We self-consistently determine four freeze-out points from preliminary results of the STAR Collaboration. Comparing the experimental data with the PDM results along these four points, we find that the model describes the low energy ( $s_{N N} ≲$ 4 GeV) data well. This suggests that nucleon interactions and the LG phase transition may contribute significantly to the fluctuations in low energy heavy-ion collisions.
nucl-thhep-ph
09
QCD phase structure at high baryon density
Agnieszka Sorensen
Heavy-ion collisions provide unique access to the properties of QCD matter over a broad range of temperatures and baryon densities. We review recent progress in constraining the high-density phase structure of QCD, with particular emphasis on the microscopic inputs required for reliable transport modeling. We discuss cluster production, strange-particle interactions, collision dynamics at few-GeV energies, and the isospin dependence of the nuclear interaction, together with their impact on the interpretation of flow, yields, fluctuations, and possible critical signatures.
nucl-th
10
Including Thermal Mesons and Meson Resonances in the Chiral Mean-Field Equation of State
Micheal Kahangirwe · Joaquin Grefa · Mateus Reinke Pelicer · Rajesh Kumar · Claudia Ratti · Veronica Dexheimer
The Chiral Mean-Field (CMF) model describes dense matter in terms of baryons and quarks interacting through scalar and vector meson mean fields. In the mean-field approximation, the meson fields are replaced by their expectation values. Their role in generating interactions and in-medium properties is retained, but explicit thermal mesonic excitations are absent. This becomes increasingly problematic at high temperature, where mesons contribute significantly to the thermodynamics of hadronic matter. Here, we keep the original CMF description of dense matter and add the thermal mesonic degrees of freedom using the mesonic sector of the Hadron Resonance Gas (HRG) module in the MUSES framework. Ground-state pseudoscalar and vector mesons account for the missing thermal excitations, while mesonic resonances provide, within the HRG picture, an effective description of mesonic interactions through resonance formation. We study how these contributions affect the pressure, entropy density, energy density, and baryon density, and compare the resulting equation of state with continuum-extrapolated lattice-QCD calculations.
nucl-th
11
An Extended Chiral Mean-Field Model with Medium-Modified Thermal Mesons for Hot and Dense Hadronic Matter
Micheal Kahangirwe · Rajesh Kumar · Joaquin Grefa · Konstantin Maslov · Yuhan Wang · Arvind Kumar · Claudia Ratti · Veronica Dexheimer
In this conference proceeding we review an extension of the Chiral Mean Field (CMF) model that consistently incorporates interacting thermal mesons with self-consistent in-medium masses. In this approach, the in-medium masses of pseudoscalar and vector mesons are evaluated through the explicit chiral symmetry-breaking and vector-interaction terms in the Lagrangian respectively, before applying the mean-field approximation. These medium-modified meson properties introduce additional feedback into the CMF equations of motion, leading to a revised equation of state. The impact of this refinement is analyzed by comparing the hadronic model predictions with recent lattice QCD data and other hadronic descriptions, such as the hadron resonance gas model. The modified CMF framework, featuring an improved meson treatment (mCMF),demonstrates enhanced consistency with lattice-QCD results for thermodynamic observables across a broad range of temperatures and baryon chemical potentials.
nucl-th
12
Bayesian Inferences on Analytical Equations of State Approximations of Neutron Stars
Arijit Das · Sourav Roy Chowdhury
Equations of state (EoS) for dense matter are commonly provided in tabulated pressure-energy density relations, complicating numerical implementation and potentially compromising thermodynamic consistency. In this work, we propose a universal, piecewise-continuous functional form with a common parametrization capable of representing a broad class of dense matter EoSs. We validate this parametrization against tabulated EoSs from the CompOSE and LALSimulation repositories. Following the initial deterministic fitting, we employed two distinct Bayesian approaches: one based on synthetic EoSs generated by adding noise to the fitted EoS and another based on multimessenger measurements of neutron-star masses and tidal deformabilities. In both approaches, the initial best-fit parameters are used as reference values. For the considered EoSs, spanning from very soft to very stiff, the resulting fits reproduce the defined tabulated EoSs and the associated macroscopic neutron-star observables in the repositories with sufficient degree of accuracy. The inferred parameters exhibit strong correlations arising from the continuity conditions imposed at the segment boundaries. These correlations persist in the low- and intermediate-density segments under multimessenger inference but become weak in the core, reflecting the limited constraining power of current observations at high densities. The ability of a single functional form to describe EoSs derived from different microscopic frameworks, together with the recurrence of similar parameter correlations, suggests that diverse dense matter EoSs may share a common underlying structure.
↳ astro-ph.HEnucl-th
13
Generalized Detectors at Colliders
Mark Gonzalez · Kyle Lee · Ian Moult
Recent progress in collider physics has reformulated phenomenological questions in terms of detector correlation functions and advanced their theoretical understanding. These advances have primarily focused on correlators of the average null energy operator, $E (n)$ , known as energy correlators. However, colliders have access to a much broader class of detector operators, $E_{R}^{n} (n)$ , which measure powers of the energy on a subset of hadrons $R$ , such as charged hadrons. These generalized detectors are generically not infrared and collinear safe, and their description requires nonperturbative matching between the hadronic detectors measured in the infrared and the partonic detectors used in ultraviolet calculations. We develop a framework for computing their multi-point correlation functions. We introduce universal nonperturbative matching coefficients, termed "detector functions", that implement this infrared-ultraviolet matching. For the $E_{R}^{n}$ operators studied here, these coefficients are represented by energy-weighted moments of single- and multi-hadron fragmentation functions. We present their renormalization group structure, derive QCD factorization theorems for the projected correlators, and compute jet functions through next-to-leading order. In the fixed-coupling pure Yang-Mills limit, we derive the light-ray OPE of hadronic detectors and connect it to the QCD factorization framework. We also identify universal nonperturbative power corrections generated by soft radiation, which are enhanced in the collinear limit and can substantially modify the perturbative angular scaling. A parton shower study finds qualitative agreement with the predicted perturbative and nonperturbative scaling behaviors. Our work significantly broadens the space of detector operators under theoretical control, with potential phenomenological applications.
↳ hep-phhep-exhep-thnucl-ex+1
14
On the dynamical accessibility of twin stars
Mahdi Naseri · Vasileios Paschalidis
A sufficiently strong hadron-to-quark first-order phase transition can give rise to a third family of stable compact stars that are commonly referred to as hybrid hadron-quark stars. Stable hybrid stars that have the same gravitational mass as neutron stars are referred to as twin stars. Although equilibrium twin stars may exist, whether they can be dynamically formed remains an open question. We investigate this problem by examining the gravitational binding energy of competing equilibrium configurations at fixed baryonic rest mass and by performing general relativistic hydrodynamical simulations of several possible transition channels. While twin stars are more gravitationally bound than neutron stars with the same rest mass, this energetic preference alone does not determine the dynamical outcome. Compression and shocks during the evolution generate thermal pressure that can prevent the system from settling on the cold twin star branch. Our simulations show that sufficiently rapid cooling can remove this thermal support and enable twin star formation, whereas slower or no cooling generally favors a neutron star remnant. Accessing the twin star branch through the formation channels considered here requires cooling on a timescale comparable to or shorter than the stellar dynamical timescale. Since realistic cooling mechanisms operate on much longer timescales, our results suggest that in channels that conserve the total rest-mass neutron stars may be dynamically favored even when a more gravitationally bound twin star configuration exists with the same rest mass. Our results demonstrate a point of principle, at least for equations of state where the quark deconfinement density does not change appreciably for temperatures up to $10 - 20 MeV .$
↳ astro-ph.HEgr-qcnucl-th
15
Dark Matter Inelastic Scattering with Nuclei for Direct Detection
Shao-Feng Ge · Oleg Titov · Yakun Wang
We investigate the nuclear responses for the WIMP-nucleus scattering in the dark matter direct detection with particular emphasis on the inelastic channel for the $^{129}$ Xe and $^{131}$ Xe isotopes. Our generalization incorporates both the elastic and inelastic scattering channels. With multipole expansion of the effective operators, the angular momentum, parity and time-reversal selection rules can effectively determine the allowed transitions. Instead of the nuclear shell model, we use the state-of-the-art relativistic configuration-interaction density functional theory, which is more suitable for heavy nuclei such as xenon isotopes, to calculate the nuclear response functions. For certain interaction operators, the inelastic contribution can be comparable as its elastic counterpart and some can even dominate by up to three orders of magnitude. Additionally, the higher excited nuclear states can have comparable signal rate as the first excited states. We compare our results with the nuclear shell model calculation. The differences would have significant effects for interpreting the dark matter direct detection searches.
↳ hep-phnucl-th
16
Diffusivity in Dissipative Quantum Transport from an Exactly Solvable Krylov Chain
Zhi-Li Zhou · Jorge Noronha
The computation of transport coefficients in interacting quantum many-body systems is rarely analytically accessible. Here, we develop a new Krylov-space mechanism that makes the leading density dependent correction to Green-Kubo diffusivity \emph{exactly} calculable in the strong-dissipation regime of a one-dimensional noisy spin- $\frac{1}{2}$ XXZ chain. This is done by showing that the density-polarization-dressed bond coherence generates a Krylov subspace where repeated action of the dissipator closes exactly on an explicitly identifiable operator family. Within this subspace, the dissipative dynamics is then mapped onto a self-similar semi-infinite chain with a boundary defect. Surprisingly, \emph{all} Lanczos coefficients of the Krylov chain and its boundary Green's function can be determined exactly. The latter then determines the exact leading density-dependent correction to the diffusivity. Finally, we calculate analytically the full boundary-to-bulk Green's function and find that it decays exponentially along the emergent Krylov chain.
↳ cond-mat.stat-mechhep-thmath-phmath.MP+2
17
Supernova nucleosynthesis: a review
Shuai Zha · Yudong Luo · Zhanwen Han
Supernovae are major drivers of cosmic chemical evolution. They synthesize heavy elements and disperse them into the interstellar medium via their explosion shocks. Light elements are converted into heavier ones during both presupernova evolution and the explosive event itself. Supernova explosions generate nucleosynthesis environments rich in neutrons, protons, and neutrinos under unique thermodynamic conditions, which can enable the production of heavy elements beyond iron. Modern numerical simulations are constructing increasingly realistic explosion models of various supernova channels, providing more accurate nucleosynthesis conditions and chemical yields. In tandem with advances in large-scale spectroscopic surveys delivering precise, high-resolution stellar abundance data, as well as isotopic ratios from presolar grains and meteorites, our understanding of the supernova role in cosmic nucleosynthesis is poised to advance significantly. We review recent progress in modeling various supernova channels, with particular emphasis on nucleosynthesis yields derived from state-of-the-art simulations. We examine the roles of Type Ia, core-collapse, electron-capture, and pair-instability supernovae in producing intermediate-mass, iron-peak, trans-iron, and very heavy elements, as well as their characteristic chemical imprints. We also outline major theoretical uncertainties that affect yield predictions. We intend this review to serve as a timely reference for theoretical model development and a practical guide for interpreting observational abundance data.
↳ astro-ph.HEastro-ph.SRnucl-exnucl-th
18
Constraining Proton Spin at Small $x$ with Valence Quark Model
Yossathorn Tawabutr · Daniel Adamiak · Heikki Mäntysaari
Recently, a global analysis has been performed for longitudinal spin asymmetries in polarized deep inelastic scattering (DIS) processes, combining the polarized valence quark model with the large- $N_{c} & N_{f}$ helicity evolution equations. With a three-fold reduction in the number of free parameters, the valence quark model results in a six-fold reduction of uncertainty for the resulting prediction of total parton spin inside the proton, when compared to previous analysis performed with traditional moderate- $x$ model inspired by Born approximation. The fit based on valence quark model predicts a positive gluon hPDF and negative $g_{1}$ structure function at small $x$ . However, the resulting increase in the $χ^{2}$ -statistic of the fit warrants further examination into the physical uncertainty of the valence quark model, which is a work in progress. We also summarize other possibilities of future research directions towards the end of this article.
↳ hep-phnucl-th
19
Searching for new physics with contact-free transitions in muonic atoms
Noam Burger · Ben Ohayon
We present a feasibility study demonstrating how recent advances in quantum-sensing technologies can facilitate stringent comparisons between theoretical predictions and experimental measurements of \emph{contact-free} transitions in muonic atoms. Such comparisons can probe previously unexplored regions of the parameter space governing spin-independent muon-proton interactions and disentangle the extraction of fundamental constants from searches for physics beyond the Standard Model.
↳ hep-phhep-exnucl-exnucl-th+1
20
Double parton scattering off nuclei and the double-EMC effect
Filippo Fornetti · Federico Alberto Ceccopieri · Emanuele Pace · Matteo Rinaldi · Giovanni Salmè
The double-parton scattering process off light and heavy nuclei is proposed as an effective tool to open a novel window for accurately studying the effects of nuclear binding on the internal structure of the nucleon, in the spirit of the European Muon Collaboration (EMC) effect. The key ingredient is the actual calculation of nuclear double-parton distributions that contain information about double-parton distributions and generalized-parton distributions of the nucleon, folded with nuclear light-front distributions. It allows to introduce a new quantity, which we call double-EMC ratio that appears to be much more sensitive than the standard EMC effect to both the nucleon partonic structure and to the nuclear binding. Hence, it could help solving long-standing questions about how nucleons change when they are bound in atomic nuclei.
↳ hep-phnucl-th
21
Matching relations for gluon TMDs up to one-loop accuracy
Alessio Carmelo Alvaro · Nanako Kato · Barbara Pasquini · Cristian Pisano · Simone Rodini
We present new results on the matching relations for gluon transverse momentum dependent parton distribution functions up to one-loop accuracy. At tree-level, employing the spinor formalism, we obtain these relations up to twist 3 accuracy for both T-even and T-odd distributions, including the hadron-mass corrections. At one-loop order, we extend the parton-in-parton approach to include higher-twist operators in the small- $b$ expansion. As a result, we derive for the first time the Wandzura-Wilczek relation for the worm-gear T distributions and establish a systematic method to include mass corrections at one-loop and twist-2 accuracies.
↳ hep-phhep-thnucl-exnucl-th
22
Quark fracture function at small $x$ from the Color Glass Condensate
Paul Caucal · Nolann Juet · Farid Salazar
The target-fragmentation region in deeply inelastic electron-nucleus scattering provides insight into the partonic structure of the target, as hadrons measured in the final state retain information about the nonperturbative dynamics of spectator partons inside the nucleus. In QCD factorization theorems, this nonperturbative dynamics is encoded in objects known as fracture functions. In this paper, we study the extended quark fracture function in the limit where the struck (anti)quark carries a very small longitudinal momentum fraction, $x$ . We first present an elementary derivation within the Color Glass Condensate effective field theory of the quark fracture function in terms of the dipole operator at small $x$ . At the parton level, the quark extended fracture function is sensitive to gluon saturation when the transverse momentum $P_{⊥}$ of the outgoing parton produced in the target-fragmentation region is smaller than the nuclear saturation scale $Q_{s}$ , in which regime the $P_{⊥}$ distribution becomes approximately flat. We then show, through a numerical study that incorporates the convolution of this parton-level result with a collinear fragmentation function, that hadronization largely washes out these saturation effects, as the convolution predominantly probes partonic transverse momenta that are typically larger than $Q_{s}$ .
↳ hep-phnucl-th
23
The Interplay Between Electromagnetic Fields and Baryon Stopping in a Hydrodynamic Model for Charged Flow
Tuna Demircik · Dmitri E. Kharzeev · Krishna Rajagopal · Raimond Snellings
Charge-dependent directed flow provides a sensitive probe of early electromagnetic fields and baryon stopping in relativistic heavy-ion collisions. Recent STAR measurements show a centrality-dependent sign change in the directed flow splitting (the difference between the directed flow of protons and antiprotons), indicating that electromagnetic effects alone are not sufficient to describe this observable and that the baryon stopping $-$ in particular the component of the stopped proton distribution that is odd in rapidity and odd under reflection in the impact parameter direction $-$ must also be included. We develop a semi-analytic hydrodynamic framework that combines spectator-induced electromagnetic fields with a Glauber-based description of baryon stopping, built upon an analytic solution for the background hydrodynamic flow due to Gubser together with the simplifying assumption of a constant electrical conductivity. For Au+Au collisions at $s_{N N} = 200$ GeV, we find that baryon stopping gives a positive contribution to the directed flow splitting that decreases for more peripheral collisions, while electromagnetic fields give a negative contribution that is larger for more peripheral collisions. The competition between these two effects naturally reproduces the observed sign change in Au+Au collisions as a function of centrality, describes the observed rapidity dependence in the $50$ -- $80%$ centrality interval, and reproduces trends seen in U+U collisions. Although the simplifying assumptions that we have made regarding the analytic background and constant conductivity limit our ability to make quantitative comparisons, our model provides a transparent explanation of how transported baryon number and spectator-induced electromagnetic fields jointly shape charge-dependent directed flow.
↳ hep-phhep-thnucl-exnucl-th
24
Comment on "Non-Monotonicity of Transverse-Momentum Correlations in Au+Au Collisions at RHIC"
Roy A. Lacey
Recent measurements of two-particle transverse-momentum correlations, $C_{p_{T}}$ , in Au+Au collisions have revealed a statistically significant non-monotonic beam-energy dependence over the range $s_{N N} = 3.0$ -- $7.7$ ~GeV that has been interpreted as potentially indicative of critical phenomena associated with a critical end point (CEP) in the QCD phase diagram. This interpretation is assessed in light of the absence of a controlled framework establishing $C_{p_{T}}$ as a quantitative proxy for the underlying critical response. The implications of this limitation are examined by considering the expected finite-size and finite-time modification of critical fluctuations, substantial non-critical dynamical contributions, the lack of demonstrated critical scaling, and the sizeable discrepancy between the CEP region inferred from the observed $C_{p_{T}}$ non-monotonicity and that constrained by susceptibility-based measurements and finite-size scaling analyses. Taken together, these considerations indicate that the observed $C_{p_{T}}$ non-monotonicity does not, by itself, establish a critical origin nor provide reliable quantitative constraints on the existence or location of a possible CEP.
↳ nucl-exhep-exhep-latnucl-th
25
Rotational Brownian Motion and $J/ ψ$ Spin Alignment in Heavy-Ion Collisions
Bhagyarathi Sahoo · Captain R. Singh
The heavy-quark polarization in ultra-relativistic heavy-ion collisions (HICs) serves as a probe for unfolding the characteristics of deconfined QCD. The present study explores the spin alignment of $J/ ψ$ in the HICs by employing the rotational Brownian motion of charm quarks in the presence of a strong magnetic field. We derive an analytical expression for the polarization of the $c$ - $c ˉ$ pair based on the Fokker-Planck equation under the consideration of spin-vorticity coupling. These polarized $c$ - $c ˉ$ pairs lead to the formation of the $J / ψ$ at the hadronization surface via the coalescence and fragmentation mechanisms. Correspondingly, we obtain the $m = 0$ diagonal element $ρ_{00}$ of the $J / ψ$ spin-density matrix, which quantifies its spin alignment along the chosen quantization axis. Our study provides a microscopic description of heavy-quark spin transport and suggests rotational diffusion as a possible mechanism underlying the observed $J / ψ$ spin alignment.
↳ hep-phnucl-th